There are two main quick charging approaches in the supply of power from an adaptor to a portable device through a USB (Universal Serial Bus) cable. For example, if the portable device requires 30 W, one approach is to apply 10V, 3 A. Another approach is to apply 5V, 6 A. For such high current charging, temperature measurement can be adopted on the USB cable because the connector for the adaptor is typically a ‘Std-A plug’ and the connector for the portable device is typically a ‘Micro-B plug’ as show in FIG. 1, which shows a typical connection for a conventional adaptor and portable device using a standard-A to micro-B USB cable. Circuitry for temperature monitoring can be designed and resides in the Micro-B plug.
With the introduction of the ‘Type-C’ USB cables, it will be a challenge to know which side of the plug (1 or 2) is connected to the portable device side as shown in FIG. 2, which shows a typical connection for a conventional adaptor and portable device using a USB Type-C to Type-C cable. It is known that either plug can be used, as the plugs are interchangeable.
One conventional temperature monitoring approach for USB Type-C cables is to include two so-called ‘eMarker ICs’ in both plug locations (1 and 2), so as to monitor the temperature of the cable as shown in FIG. 3 and FIG. 4. FIG. 3 shows a first conventional solution for supporting temperature monitoring in USB Type-C cables. FIG. 4 shows a second conventional solution for supporting temperature monitoring in USB Type-C cables.
An eMarker IC for USB Type-C cables includes a controller and additional electronics such as re-drivers for re-conditioning high-speed USB data signals. In active cable designs, each end of the cable can have different active functions. A DFP (Downstream Facing Port) queries the cable to know the features supported at each end of the cable.
One conventional temperature monitoring approach for USB Type-C cables is to include an eMarker IC in both plug locations, so as to monitor the temperature of the cable as shown in FIG. 3 and FIG. 4. Such a solution requires a power distribution switch in each plug for isolating the VBUS line on both sides of the USB cable in the event of an over-temperature condition. The VBUS line in USB is a wire which carries a nominal 5V supply. By including two power distribution switches and two eMarker ICs in a USB Type-C cable, system cost is increased as the cable manufacturer must ensure that the cable meets the cable IR drop requirement of USB Type-C specification between source and sink as shown in FIG. 5.
As such, there is a need for a more cost effective temperature sensing technique for USB Type-C cables.